A broad range of electrical conductors and electrical cables are installed in modern buildings for a wide variety of uses. Such uses include, among others, data transmission between computers, voice communications, video communications, power transmission over communications cables, e.g. power over Ethernet, as well as control signal transmission for building security, fire alarm, and temperature control systems. These cable networks extend throughout modern office and industrial buildings, and frequently extend through the space between the dropped ceiling and the floor above. Ventilation system components are also frequently extended through this space for directing heated and chilled air to the space below the ceiling and also to direct return air exchange. The horizontal space between the dropped ceiling and the floor above is commonly referred to as the “plenum” area. Similarly, the vertical space of the walls between the floor and the ceiling include the networking of the aforementioned cable types. These vertical spaces are generally called the “riser” cabling space. Electrical conductors and cables extending through plenum areas are governed by special provisions of the National Electric Code (“NEC”). Cables intended for installation in the air handling spaces (e.g., plenums, risers, ducts, etc.) of buildings are specifically required by NEC/CEC/IEC to pass flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FT-6. The UL-910, FT-6 and the NFPA 262, which represent the top of the fire rating hierarchy established by the NEC and CEC, respectively. Also applicable are the UL 1666 Riser test and the IEC 60332-3C and D flammability criteria. Cables possessing these ratings, generally known as “plenum” or “plenum rated” or “riser” or “riser rated”, may be substituted for cables having a lower rating (e.g., CMR, CM, CMX, FT4, FTI or their equivalents), while lower rated cables may not be used where plenum or riser rated cables are required.
Many communication systems utilize high performance cables. These high performance cables normally have four or more twisted pairs of conductors for transmitting data and receiving data. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs. Other high performance cables can include coaxial cables, e.g., used singly or in conjunction with twisted pairs as a composite cable.
In a conventional cable, each twisted pair of conductors has a specified distance between twists along the longitudinal direction. That distance is referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist directions. Such close spacing increases the amount of undesirable energy transferred between conductors, which is commonly referred to as cross-talk. Undesirable energy may also be transferred between adjacent cables (which is known as alien crosstalk) or alien near-end cross talk (anext) or alien far-end cross talk (afext).
The Telecommunications Industry Association and Electronics Industry Association (TIA/EIA) have defined standards for crosstalk, including TIA/EIA-568 A, B, and C including the most recent edition of the specification. The International Electromechanical Commission (IEC) has also defined standards for data communication cable cross-talk, including ISO/IEC 11801. One high-performance standard for 100 MHz cable is ISO/IEC 11801, Category 5, or more recently referred to as Category 5e. Additionally, more stringent standards have been implemented for higher frequency cables including Category 6, augmented Category 6 (Category 6A), Category 7, augmented Category 7 (Category 7A) which are rated for frequencies in the range of 1 MHz through 1 GHz.
There remains a need for communications cables that can operate reliably while minimizing or eliminating cross-talk between conductors within a cable or alien cross-talk between cables, and also a need for separators for use in such telecommunications cables. There also remains a need for communications cables that can provide low smoke generation and overall flame retardancy, as required by the “NEC” for use in plenum and riser areas of a building.